nm-applet is currently not designed to run in such a restricted mode which would make it safe to expose to unprivileged users.
It's a bug of the login screen to run an application that is not suitable for the security constraints of the login process.
It would be interesting to add a --restricted mode to nm-applet, but I wouldn't call that a bug. It's a missing feature. Until that feature is implemented, it's up to login screen not to use nm-applet.
It's not really a nm-applet issue.
nm-applet is currently not designed to run in such a restricted mode which would make it safe to expose to unprivileged users.
It's a bug of the login screen to run an application that is not suitable for the security constraints of the login process.
It would be interesting to add a --restricted mode to nm-applet, but I wouldn't call that a bug. It's a missing feature. Until that feature is implemented, it's up to login screen not to use nm-applet.